Matthew Poole and continuators on 1 Samuel 17:38

38 ¶ And Saul armed David with his armour , and he put an helmet of brass upon his head, also he armed him with a coat of mail.

Either, 1. With Saul's own Armour which he used to wear in Battel: which seems not to agree with the extraordinary height of Saul's Stature, 1 Sam. 10. 23. Nor is it like that Saul would disarm himself, when he was going forth to the Battel, v. 20, 21. Or, 2. With Armour taken out of his Armory. Not that the whole Armory of Saul was brought into the Field; but that some chosen Arms were taken out thence, and brought for any emergent occasion. Or rather, 3. With his vestments, or garments. For, 1. So the Hebrew Word properly and usually signifies; and so this same Word is Translated, 1 Sam. 18. 4. 2. His Armour is distinguished from this, and is particularly described in the following words. He seems therefore to speak of some Military Vestments which were then used in War, and were contrived for defence; such as Buff-coats now are.

Marginal references: Heb. clothed, &c. with his clothes.